Some integrated circuits include input/output (I/O) cells located in I/O rings close to the outer edge of the integrated circuit. The I/O cells are used to receive input signals from external devices and to output signals to external devices. In such an integrated circuit with an I/O ring, voltage detector circuits can be used to tri-state the I/O cells to place them in a high impedance state during power-up and/or power-down of the integrated circuit to prevent potential crowbar current in the I/O output driver. These voltage detectors, for example, can be used within microcontroller integrated circuits to allow the microcontroller to be powered-up or powered-down in any sequence. For example, where a core power supply voltage and a different I/O power supply voltage are used, the core supply voltage can be powered-up before or after the I/O power supply is powered-up. In prior solutions, however, these voltage detector circuits have had large space and high power requirements. Further, prior detector solutions have single power supply voltages that are used for core circuitry, the voltage detector, and I/O ring.